The present invention relates to a controller for an electric machine, in particular for a linear motor.
To ensure clarity, the term “electric machine” should not be limited in the disclosre to a linear motor, but should be construed to also include, for example, a torque motor or a synchronous motor or a synchronous generator.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
A motor controller and a method for controlling and operating electric machines, such as motors, to allow rapid and accurate control of movement of the electric machine is described, for example, in European Pat. No. EP 0 902 918 B1. The controller has a memory which stores at least one physical parameter, such as a magnetic field parameter, to control the electric machine or the linear motor. It is further known from U.S. Pat. No. 5,091,665 to provide a Hall sensor for determining the position of a machine or a machine section. The sensor for determining the position is hereby a separate element of the primary section.
Physical parameters of the afore-described type are described, for example, in Chapter 2 of the Operating Manual SIMUDRIVE 611 digital and/or SINUMERIK 840D/810D. An example of a physical parameter is a parameter that relates to the magnetic field of the permanent magnets. This parameter is referred to, for example, also as a force constant or a Force-Current-Ratio.
Technical advances require a much higher precision in controlling electric motors. If the underlying physical parameters on which the control of an electric machine is based change, then the quality of the control deteriorates. However, not every physical parameter that can be used to control an electric motor is subject to change during the operation of the electric machine. For example, the number of poles of the electric machine is a physical parameter which can be used in the controller. However, the number of poles will not change during operation of electric machine. However, this is different for, for example, the physical parameters that relate to the magnetization the permanent magnets. The strength of the magnetic field of permanent magnets can change, for example decrease, during the service life of the electric machine. The change in the magnetic field strength of permanent magnets of a motor section can also be influenced by environmental factors, for example an accumulation of dirt or of other magnetic materials that affect the magnetic field lines of the permanent magnets. Parameters that depend on the magnetic field strength of the permanent magnets and are stored in the controller for controlling the electric machine then no longer correspond exactly to the actual magnetic field strength produced by the permanent magnets.
As a result, the accuracy of the control of electric machine or the linear motor is changed. Moreover, a parameter then depends on the magnetic fields strength of a permanent magnet or on the air gap can be subject to manufacturing tolerances and therefore be from a corresponding parameter of a prototype of an electric machine or a linear motor.
It would therefore be desirable and advantageous to provide an improved controller for a motor and an improved method for parametrizing an electric motor, which obviates prior art shortcomings and is able to specifically allow a more precise control of the electric motor.